The ozonation of pyrene: Pathway and product identification

The pathway by which ozone reacts with pyrene, a polycyclic aromatic hydrocarbon (PAH), is proposed in this paper. Pyrene was dissolved in a 90% acetonitrile:water (v/v) mixture. At this ratio, sufficient water is present to participate in the ozonolysis reaction and thereby mimic what occurs in pure water. The initial pyrene concentration was 5 mM. The ozone dosages were varied to obtain different extents of reaction. A stoichiometric ratio of 1.68 mol ozone mol(-1) pyrene was required to completely destroy pyrene. The ozonation products were tentatively identified by gas chromatography-mass spectrometry (GC-MS). Fourteen products including aldehyde and carboxylic acid substituted phenanthrene- and biphenyl-type oxidation products were identified. Several ring-cleavage reactions occurred sequentially: (i) ring cleavage of pyrene first occurred at the 4,5 position, with phenanthrene-type products predominating; and (ii) once secondary ring cleavage occurred, the concentration of pyrene and the phenanthrene-type products,decreased dramatically, while the concentration of biphenyl-type products increased. The oxidation of pyrene by hydroxyl free radicals was found to be involved in the reaction, even at pH 3.7. (C) 1998 Elsevier Science Ltd. All rights reserved.